Infant-mother attachment security and cortisol reactivity during the strange situation procedure: Longitudinal associations with maternal depressive symptoms and infant temperament

Abstract

This study examined the influence of infant-mother attachment security on the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and cortisol stress responses in 14-month-old infants. Eighty-two mother-infant dyads participated in the Strange Situation Procedure (SSP), with salivary cortisol sampled across four time points. Infant attachment security, maternal depressive symptoms, and infant temperament were assessed longitudinally over the first postnatal year. Infant cortisol trajectories differed by attachment security: insecurely attached infants had significantly higher baseline cortisol, which declined following the SSP, whereas securely attached infants had lower baseline cortisol and a trend toward increased cortisol post-stressor. Maternal cortisol declined over time for all groups, with no differences between mothers of secure and insecure infants. Mothers of securely attached infants experienced sub-clinical depressive symptoms at 32 weeks pre-partum, with a decline of symptoms to a normal range during the first year postpartum. Negative infant temperament increased over the first year but was not associated with attachment security or cortisol response. These findings demonstrate that infant-mother attachment quality shapes infant HPA axis regulation independent of maternal depressive symptoms or negative infant temperament, suggesting the importance of early identification and intervention for attachment difficulties to promote adaptive stress physiology in infants.